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Patented Dee. aaieas. g 1,556,342

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HARRY NY QUIST, F ELM I-IURST, NEW YORTQ ASSIGNOR TO AMERICAN TELEPHONEi AND TELEGRAPH COMPANY, A COBIE'ORATEON OF NEW YORK.

MEANS FOR monnasme rownn oarnorrv or aa-rvrn REPEATERS/ Applicationfiled June 27, 1 923. Serial No. 648,069. I

To all whom it may concern: ments of the invention. Figs. 4, and 6 Be itknown that I, HARRY NYQUIST, reshow indetail the circuit arrangementsand siding at Elmhurst, in the county of Queens impedance relations ofFigs. 1, 2 and 3 re- '55 and State of New York, haveinventedcerspectively. Similar reference characters 5 tain Improvements in Meansfor Increasing have been utilized to denote like parts in-all PowerCapacity of 22-Type Repeaters, of of'the figures of the drawing. Fig. 7is a which the following is a specification. schematic diagram whichaccompanies cer- This invention relates to im rovements in t ainmathematical com utations iven to ilrepeater circuitsand moreparticularly to lustratethe principles of the invention. 1 arrangementsfor increasing the power ca- In Fig. 1 is shown a circuit including apacityjof vacuum tube repeater circuits. vacuum tube 1 having grid,filament and -When a battery with a fluctuating voltage plateelectrodes. The circuit is connected is utilized to supply potential tothe plate through a transformer 2 to aline L. Inthe circuit of a vacuumtube repeater the gain arrangement shown it will be assumed that .15, ofthe repeater would have a tendency to steady battery Will bejutilizedfor supply-,

35 manner despite the fact that a supply batbe irregular as thefluctuating battery would ing potential to the tube, or in other words,

tend to vary the internal impedance of the a battery which will not besubject to volt tube, which in turn would tend to vary its agefluctuations. The internal impedance of output impedance uponwhich thegain 'dethe tube will be assumed to be 6000 ohms.

2o pends. it has accordingly been the practice The ratio of thetransformer 2 will be ad to include in the output circuit of the tubejusted so that looking out toward line-L the a series resistance havingan impedance relaimpedance will be 6000 ohms. The. potentively largewithrespect to the internal imtial drop across the output circuit of thepedance of the tube so that the total output tube atpoints on line 5, 6,will be a which 25 impedance would not be varied to any apwill be 1/2 Vwhich is the internal voltage preciable extent by a variation in theinat full load. This will hold true because ternal impedance of the tubeitself. This the impedance looking into the transformer seriesresistance, however, will cause an un 2 will be 6000 ohms which is 1/2of the total desirable llfitllSHllSSlOIl 1085 in tllQ (JlICllllJ. Itseries j npedance of the plate. circuit By 0 is in general the object ofthis invention to th power it f th amplifyin obviate the use of thisobjectionable series r anqemehts i a t th f l o d resistance, whileatthe same time increasing i h t t transformen Thi POWQY h of the Vacuumtube may be expressed as T02R1 whereR:the cult and causing it to operatein a stable impedamerlooking into the Output trans former, T the platecurrent, and Vzthe applied voltage. From the values assumed heretoforeit will be seen that 1%:6000 ohms,

tery is utilized which may have a fluctuating voltage. The objects ofthe invention may be accomplished by a novel adjustment and relation ofthe impedance elements of and f=V 40 the circuit which may be more fullyunder- V/2 V stood from the detailed description herein- I== I aftergiven.

The invention may be more fully underand therefore stood from thefollowing description to-' 45 gether with the accompanying drawing in vRI=60OO V2 V2 Figures 1, 2, 3, 4., 5, 6 and 7 of Which the v I 2 24000invention is illustrated. F1gs. 1 and 2 illus- Accordingly the Outputpower capaitv f trate schematically the lmpedance relations theamplifying circuit in Fig 1, which and operating characteristics ofarrangebe termed case-A is 50 ments of the prior art, while Fig. 3 showsv 2 schematically the impedance relations and V operatingcharacteristics of the, arrange- 22160-0.

In Fig. 2 is shown a tube 1, which may be assumed to be supplied withpotential from a battery whose voltage will fluctuate. To prevent theoutput impedance of the tube from varying materially because offluctuations in the internal impedance due to the battery fluctuations,there is inserted in series in the plate circuit of the tube arelatively large impedance, such as 12000 ohms, as heretofore explained.The internal impedance of the tube may be taken as approximately 6000ohms. To avoid reflection losses as will be explained hereinafter theimpedance looking out toward the line through the transformer will nowbe made 18000 ohms by suitable adjustment of the ratio of thetransformer. The drop 4) across the transformer will now be 1/2 V asbefore. The power capacity of the amplifying arrangementwill be R1 Fromthe values assumed heretofore it will be seen that RzlSOOO ohms @zV/Qaccordingly v and therefore lull (36OO0) 720O0 Accordingly the outputpower capacity of the amplifying arrangement in Figure 2 RP 18000 X willbe seen that the useful energy of a repeater of this type will be muchless than that of Fig. 1.

In the arrangements of the invention, shown schematically in Fig. 3,fluctuating battery supplies the voltage for the tube 1, whose internalimpedance is approximately 6000 ohms. The series resistance heretoforeincluded in the plate circuit is omitted but the ratio of thetransformer is changed so unit the impedance looking into the trans"iormer 2 is increased by the same amount as the series resistance. inother words this impedance is raised from 18000 ohms to 30000 ohms.lVith these values it will be clear that any variation in the internalimpedance of the tube due to voltage fluctua which may be termed case B,is It tions will cause comparatively litle effect due to the fact thatthe total output impedance is relatively so much larger than theinternal tube impedance. With the above impedance values it may be seenthat 11230000 However i; will equal as the impedance looking into thetransformer 2 is 80000 ohms which is 5/6 of the total impedance If wenow take the three values thus ascertained for the output power capacityof the amplifiers in cases it, B, and we will find them to be r r d r24.000 72000 43200 respectively. By reduction the ratio be- 5 2 2 A, gfor B, and for C. From comtween these values will appear as for parisonwith the amplifiers in case A, which due to the steady battery will havethe greatest power capacity or power output, it will be seen that incase B the amplifier will only have 1/3 the power capacity or poweroutput of case A while in case C the amplifier will have 5/?) the energyoutput of case A. In other words the amplifier in case C will give 1-2/3times the energy output of the amplifier in case l%. in this connectionit should be noted that while the arangements of case A are idealnevertheless such an arrangement can not be used with fluctuatingbattery and hence the arrangement of the present invention is of markedadvantage where fluctuating plate potentials are employed.

In Figs. l, 5 and 6, respectively are shown circuit diagramsillustrating the principles of cases A, B and C heretofore described asapplied to two way two element repeaters. In each figure the line L andbalancing network i are shown having an impedance of 1800 ohms. forpurposes of illustration. The line includes a three rr'indingtransformer 2. Connected to one of the windings of the transformer isthe output of a vacuum tube 1 and included in a circuit bridged acrossthe mid-points of windings of the transformer is a potentiometer 7, atransformer 8, and the input of a vacuum tube 9. The output of the tubesmay be assumed to have internal impedances of approximately 6000 ohms.In Fig. 4.. in Fig. 1, the ratio of the transformer will be adjusted sothat its impedance loolrhig out into line L and artificial line X willbe ohms to 6000 ohms as viewed at points on line 5, 6.

In other words the impedances looking in both directions at a point suchas on line a the impedance looking in both directions at a point suchason line 10, 11 will be equal. Under these conditions the passiveimpedance of the whole repeater will be substantially equal to that ofthe line as indicated at line 3,4 and there will be no reflection loss.The reasons for this and the impedtime value to be given thepotentiometer unspect to amplifier 1 and hence the transformer 2 willoperate to step 3600 ohms up to 18000 ohms. The ratio of tranformationbetween the combined impedance of tube 1 and resistance 13 and the otherimpedance of the plate circuit will be 18000 ohms to 18000 ohms asviewed atpoints on line 5, 6. In other words the impedances looking bothways at a point such as on line 5, 6, will be equal. The impedance atpoints 10-11looking into the line and network will be 900 ohms as theimpedances of 1800 ohms each of the line and network in this respect areconnected in parallel. Accordingly the impedance looking into thepotentiometer will be made to match this so that the impedance ratioacross line 10, 11 will be the same as the ratio across line 5, 6. Inother words the impedance looking in both directions at a point on line10, 11 will be equal. Under these conditions the passive impedance ofthe whole repeater will be substantially equal to that of the line asindicated at line 3, 4 and there will be no reflection loss. for thisand the impedance value to be given the potentiometer under variousconditions will appear more fully from the mathematical discussion to begiven hereinafter.

The reasons In the arrangements of the invention shown in Fig. 6, aswell as, Fig. 3, the ratio of the transformer 2 will be adjusted so thatits impedance looking out into the line L and network N will be 30000ohms. The impedances of 1800 ohms each of line L and network N areconnected in series and hence with respect to amplifier 1 thetransformer 2 will operate to step 3600 ohms up to 30000 ohms. The ratioof transformation between the impedance of tube 1 and the otherimpedance of the plate circuit will be 6000 ohms of 30000 ohms as viewedat a point such as line 5, 6. In other words the imped- 5111i es lookingboth-ways at a point such as line 5,16 will not be matched or equal butwill be unequal. The impedance looking out from the potentiometer intothe line and network will still be 900'ohn1s as the impedances of 1800ohmseach of the line and network in this respect are connected inparallel. In order to compensate for the impedance irregularityat'points 5-6 of the output circuit of tube 1, a similar irregularityshould be introduced at points 1011 and accordingly the impedancelooking into the transformer will in this instance be made 4500 ohms.Under these conditions the pits sive impedance of the repeater will besubstantially equal to that of the line as inclicated at 3, 4c, andthere will be no reflection loss atthis point. The reasons for this willappear from the following mathematical discussion. I I

In connection with Fig. 7 there are given some computations on thepassive impedance of a two way two element repeater on the assumptionthe impedances. of the tubes, balancing network and the potentiometermayhave arbitrary values. More specifically the computations are given sothat it may be determined what impedance should be given to thepotentiometer in order to have the passive-impedance of the repeatersubstantially equal to the line impedance when the balancing network ismade equal to the line impedance and the ratio of transformationbetweenthe tube impedance and the other impedances is altered from theusual value as in Fig. 6. In the arrangements of Fig. 7 it is assumedthat the hybrid coil'is symmetrical. Z represents the impedance of thetube 1, Z, the impedance of the potentiometer 7, and Z that of thebalancing net work; 12- is the ratio of the number of turns in the tubecircuit to the total number of turns on all the other windings. 1,, 1,,I and I are the currents in the parts of the network indicated in thefigure. c represents the voltage across one half of the line windings,as indicated. E is the voltage impressed on the network. It will beappareDnt that the passive impedance Z equals 4 I The procedure todetermine this ratio will be to set up simultaneous equations relatingthe quantities E 6, I 1 I and I and to eliminate all these quantitiesexcept E and The ratio can then be determined immediately from theresulting equation.

From an inspection of Fig. 7 it will be apparent that the followingrelations may be written down:

L224 6 a 2n (3) E1 6 'i" 1323 O This gives a total fire equationsbetween six unknown and hence by ordinary algebra tour of six unknowncan be eliminated, leaving a relation between E, and 1,. Solving thisrelation gives the passive impedance (which is the value it would haveto have to make line and network look like 30000) this becomes l. 41cult comprising a line, an amplifier having its output circuittransmitting to the line through a hybrid coil whose ratio is ad jnstedto make the impedance looking into the coil large as compared with theimpedance looking into the amplifier, a second amplifier having itsinput circuit arranged For transn'iitting from the line to theamplifier, and means to make the impedance looking into the inputcircuit of said second amplifier large as compared with the impedancelooking toward the line in order to compensate for the impedanceirregularity in the output circuit of the first amplilier.

A two element two way repeater circuit comprising a line, an amplifierhaving its output circuit associated with the line through a hybridcoil, means for introducing an impedance irregularity in saidoutputcircuit, a second amplifier having its input circuit arranged fortransmitting from the line to the amplifier, means for introducing animpedance irregularity in said input circuit to counteract the impedanceirregularity introduced in said output circuit of said first mentionedamplifier.

In testimony whereof, I have signed my name to this specification this26th day of June, 1923.

HARRY NYQUIST.

